The present invention relates generally to electrical connectors for effecting reliable connections between printed circuits, and more specifically, to electrical connectors having enhanced grounding characteristics which increase the suitability of the connectors for use in high speed and high-frequency signal applications.
When an electrical connector is used to connect together high-frequency signal circuits of printed circuit boards, or a printed circuit board and a conductive wire together, a metal grounding plate is utilized as part of the connector to prevent external leakage of the high-frequency circuits at the connector. The grounding plate is located on the exterior on the insulated housing of the connector as described in Japanese Unexamined Patent Publication No. 5-217630 and Japanese Unexamined Patent Publication No. 6-84568, for example. These type connectors utilize an insulative housing, a plurality of terminals mounted within the insulative housing and a conductive metal grounding plate attached to the exterior of the insulative housing. A cross-sectional view of these connectors would reveal, in essence, a "sandwich" type structure where the insulative housing is held, or sandwiched, between the connector terminals and the grounding plate. In such a construction, the terminals tend to act as capacitors and when a high-frequency signal is applied to a particular terminal, that signal may tend to "jump" through or across the insulative housing as well as any adjacent air gap to the metal grounding plate. This phenomenon is commonly referred to in the art as capacitive coupling. The grounding plate is connected at opposite ends of the connector to grounding circuits so that any signals which are coupled to the grounding plate will pass to a groundpath and not pass to any other terminals in the connector.
However, when the high-frequency signals jump to the grounding plate and seek the grounding circuits connected thereto at the ends of the connector, the possibility exists, especially when the length of the connector is increased, that the high-frequency signal may radiate as it travels the length of the connector to the ground circuits thereat. This is known as an "antenna effect" because the grounding plate acts as an antenna and the high-frequency signals may jump or be coupled back to other terminals of the connector, resulting in mistransmission and signal error that is detrimental to the operation of the circuits and of the connector.
In the aforementioned connectors, grounding terminals are integrally formed with the grounding plate and are located at opposite ends of the connector in the longitudinal directions, so as not interfere with the solder tail portions of the connector terminals. As the length of the connector is increased, the number of terminals are also increased and the length of the antenna locally formed in the grounding plate as explained above also increases, which in turn, increases the possibility of erroneous transmission of high frequency signals to other terminals of the connector.